| | Precipitation | Soil moisture | Data sources | Explanation of terms
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Summary
Since the last drought report, July 28, 2007, more seasonable temperatures have prevailed along with much needed precipitation across much of the reporting area. However, across the Southern Region hot and dry conditions have prevailed resulting in crop moisture stress and reduced yield potentials.
Precipitation across the reporting area was lowest in the south-western and south-eastern parts of the Southern Region (less than 10 mm) and ranged to more than 90 mm across the western and east central portions of the Northern Region. Areas that received less than adequate precipitation (less than 20 mm) since the July 28th report include most of the Southern Region and the north-central parts of the Northern Region, along with of the north-central Peace Region. Elsewhere precipitation accumulations generally ranged to well above 30 mm with many areas receiving in excess of 50 mm. As fall approaches, warmer and relatively drier weather will be needed across much of the province to finish crops and insure that harvesting operations are not hampered. Late seeding crops remain at risk with respect to early frost.
Growing season precipitation accumulations to date (April 1 to August 20, 2007), relative to the long term normal, are generally at least near normal across most of the reporting area with some notable exceptions. Across most of the south half of the Southern Region, growing season precipitation is at least moderately low, with one pocket of extremely low found in the eastern parts of the M.D. of Pincher Creek and one pocket of very low in southern parts of Cardston County. Other areas of below normal accumulations can be found across the much of the north-central and northern parts of the Northern Region, where several pockets grading down to low can be found.
Since the July 28, 2007 drought report, 30-day precipitation accumulations relative to long term normal have improved significantly across most of the reporting are; however, several areas remain dry. These include most of the, south-western portions of the Southern Region (very low), and parts of the north central Peace Region (low). Another area of emerging concern is in and around the Smoky Lake County where 30-day accumulations are classified as low, but this late in the season only pastures and late seeded crops are likely to respond significantly to further, appreciable, precipitation accumulations.
Soil moisture reserves have remained at less than 25 mm across most of the Southern Region and have depleted to less than 25 mm across most of the northern parts of the Peace Region. With these exceptions, soil moisture reserves generally range from 25 to 50 mm across most of the reporting area, with some locations still retaining more than 50 mm, particularly in the western parts of the Northern and Central Region and central parts of the Peace Region. For the most part, soil moisture reserves are at least near normal for this time of year, again with the exception of the south-western parts of the Southern Region and northern parts of the Peace Region where, in many areas, reserves grade down to at least very low.
A large selection of related maps can be found at www.agric.gov.ab.ca\acis, under the Quick Viewer tab.
Current Situation
Precipitation
Precipitation since the July 28, 2007 Drought Report (Figure 1) - Precipitation accumulations ranged from less than 10 mm across most of the south-western and extreme south-eastern parts of the Southern Region to well over 150 mm across parts of the Swan Hills. Elsewhere across the reporting area, precipitation was highly variable, but generally adequate, with the exception of the north-central and northern parts of the Northern Region and the north-central parts of the Peace Region where accumulations of 10 to 20 mm were recorded.
Peace Region: Precipitation across the Peace Region ranged from 18.9 mm at the Hawk Hills AGCM station, just north of Manning, to 83.7 mm at the Grande Prairie A station, in the City of Grande Prairie. In general, the south half of the region received more than 40 mm of precipitation and the north and northeast parts of the region less than 30 mm.
Northern Region: Precipitation accumulations ranged from 1.6 mm at the Abee AGDM station in the County of Athabasca to 125.3 mm across the north-central parts of the region to more than 80 mm in the east and far western portions of the region.
Central Region: Across much of the central parts of the region, precipitation ranged from 30 to 50 mm with the eastern and western portions of the region receiving more than 50 mm.
Southern Region: Precipitation ranged from less than 5 mm at many locations across the south half of the region with large parts of the southwest and extreme southeast receiving less than 10 mm, to 38.1 mm a the Grassy Lakes IMCIN station in the M.D. of Taber. Generally greater amounts were recorded in the north and northwest, with accumulation typically between 20 to 30 mm. Under dry land conditions, this precipitation was not adequate to maintain good crop growth, particularly given the hot and dry weather experienced throughout most of July.
Growing Season Precipitation Accumulations Relative to Long Term Normal (1961 - 2005) (Figure 2) - Growing season precipitation accumulations relative to the long term normal have continued to decrease across the southern half of the Southern Region with parts of the southwest grading down to very low and extremely low. In central and northern parts of the Northern Region, growing season precipitation accumulations remain moderately low with several isolated pockets grading down to low. Elsewhere, for the most part growing season precipitation accumulations are at least near normal, with several locations in the Central Region grading up to at least high.
Peace Region: To date, growing season precipitation is at least near normal across the most of the region, with a small area confined to the extreme southwest of the County of Grande Prairie that grades down to moderately low.
Northern Region: Growing season precipitation is lowest in the north and north-central portions of the region and is classified as moderately low, with several pockets grading down to low. Elsewhere across the region growing season accumulations are generally classified as at least near normal, with parts of the southwest grading up to at least high.
Central Region: Most of the region has received at least moderately high growing season precipitation to date, with much of the west-half of the region classified as high to extremely high. Currently the driest area in the region, confined to the County of Paintearth, is classified as moderately low.
Southern Region: Much of the southern half of the region has received at least moderately low growing season accumulations to date, with the driest areas found in the M.D of Pincher Creek, currently classified as extremely low, and the southern parts of Cardston County classified as very low. Hot and dry weather over the past several weeks has lead to severe moisture stress on dry land fields resulting in significant yield reductions.
30-Day Precipitation Accumulations relative to Long Term Normal (1961 - 2005) (Figure 3) - Since the July 28, 2007 report, 30-day precipitation accumulations have generally improved over much of the Central, Northern and southern Peace Regions; however, deficits continue across most of the Southern Region and northern and eastern parts of the Peace Region. The driest areas are classified as having very low accumulations and these include south-western Alberta and parts of the north-central Northern Region, centred on Smoky Lake County.
Peace Region: Most of the south-western portions of the region have experienced at least near normal accumulations, a definite improvement over conditions that were reported during the last drought report (July 28, 2007). Across the north-central and eastern parts of the region, 30-day accumulations have declined to moderately low with a few pockets of low.
Northern Region: Most of the region has experienced at least near normal accumulations, a definite improvement over conditions that were reported during the July 28, 2007 report; however, a few pockets of moderately low can be found across the region, with the driest area (classified as very low) found in Smoky Lake County.
Central Region: Most of the region has experienced at least near normal accumulations, a definite improvement over conditions that were reported during the July 28, 2007 report. The driest areas of the region, currently classified as moderately low, are centrally located around the Highway 2 corridor.
Southern Region: Dry conditions continue to prevail with most of the region receiving moderately low accumulations, grading down to very low across much of the southwest. Across the region, yields for major grains and oilseeds are expected to be below the 10-year average. Above normal precipitation will be needed between now and spring seeding to bring soil moisture levels back to normal.
Average Precipitation Accumulations for August (Figure 4) - Historically, the first half of August is typically wetter than the last half of August and typically, this month marks the beginning of a drying trend for most of the reporting area, with the exception of the Southern Region, where July tends to mark the start of drier conditions. For August, average precipitation typically ranges from 30 to 40 mm in the southeast, to greater than 70 mm across the western parts of the Northern Region and south-eastern parts of the Peace Region.
Soil moisture in the agricultural regions of Alberta (Figure 5 and Figure 6)
Recent precipitation and a return to cooler temperatures have resulted in a slight increase in soil moisture reserves across the eastern parts of the Central and Northern Regions. However reserves continue to decline across all other parts of the reporting area, a condition that is normal for this time of year. Soil moisture recharge typically does not begin until September.
Peace Region: Soil moisture reserves are less than 25 mm across much of the north and are greatest in the central portions of the region (50 to 75 mm) Figure 5. Soil moisture reserves relative to the long term normal range from very low in the north, to moderately high in the centre, Figure 6.
Northern Region: Soil moisture levels are lowest (less than 25 mm) in the north and north-central portions of the region and grade up from 25 mm to more than 100 to 125 mm in the extreme southwest and 50 to 75 mm in the east-central portions of the region, Figure 5. Soil moisture reserves relative to the long-term normal range from low in the north and north-central portions of the region up to extremely high in the southeast and moderately high in the southwest, Figure 6.
Central Region: Soil moisture reserves are lowest less than 25 mm) in the east-central parts of the region and grade up from 25 mm to 75 to 100 mm in the extreme west and up to 50 to 75 mm in the extreme east, Figure 5. Soil moisture reserves relative to the long term normal are generally near normal across the entire region, ranging from extremely high in the southeast, to normal across most the west-half of the region, Figure 6.
Southern Region: Most of the region has soil moisture levels that are less than 25 mm (Figure 5). Generally for this time of year soil moisture reserves for most of the region are below 25 mm, however for much of the south-half of the region they have been in the less than 25 mm range since early July. This has resulted in crop moisture stress, leading to crop loss or reduced yields. Soil moisture reserves relative to the long term normal range moderately high in the northeast, down to extremely low in the southwest, Figure 6.
Data Sources:
Near Real Time Weather data
Daily and hourly near-real-time raw weather data is brought in via daily data feeds from Alberta Environment (AENV) and Environment Canada (EC). The data undergoes a preliminary computer assisted QA/QC check performed by Alberta Agriculture (AF) staff. Suspicious values are checked and verified and daily missing values are filled using archived data from AENV databases or from the EC web site. If daily data is still missing, it is estimated using data from nearby stations. Maps describing current conditions are based on preliminary data that is subject to change under further review by AF, AENV and EC.
Historical Weather data
Historical weather data was provided by Environment Canada. This data was then converted to a 10 km daily gridded weather data set that used all available daily data to generate historical climate and soil moisture normals.
Explanation of Terms
Precipitation Accumulations-Frequency of Occurrence
Precipitation accumulations, expressed as a frequency of occurrence are computed for various periods and can be found on our web site at www.agric.gov.ab.ca\acis, under the Quick Viewer tab. Maps are routinely produced for the following periods:
- Past 365-days
- Past 180-days,
- Past 90-days
- Past 30-days,
- Growing season to date -Starting April 1st
- Cold Season to date- Starting October 1st
Selected maps from this series are included in this report.
Precipitation accumulations for each period are then determined by ranking the precipitation accumulations during similar periods period dating back from 1961 to present. The current accumulation is compared to the ranked values, yielding the frequency of occurrence, based on percentiles. The percentile points were then put into arbitrary but intuitive classification fields that describe the current state as drier, near or wetter than the long term normal. The resulting map thus answers the question "how often does this occur?" The classifications are as follows:
| Description | Frequency of Occurence |
| extremely low | drier than this, on average, less than once in 25-years |
| very low | drier than this, on average, less than once in 12-years |
| low | drier than this, on average, less than once in 6-years |
| moderately low | drier than this, on average, less than once in 3-years |
| near normal | on average, this occurs at least once in 3-years |
| moderately high | wetter than this, on average, less than once in 3-years |
| high | wetter than this, on average, less than once in 6-years |
| very high | wetter than this, on average, less than once in 12-years |
| extremely high | wetter than this, on average, less than once in 25-years |
This same scheme is then used for similar maps of soil moisture and snow pack accumulations so that comparisons can readily be made across the various map types.
Snow pack (reported during the winter season only)
Snow pack snow water equivalents (SWE) are modeled for stubble fields. SWE is defined as the equivalent depth of water (mm) that the snow pack contains if it were to be melted. SWE is computed from precipitation and subsequent losses due to blowing, sublimation and snow melt processes.
In the model, if precipitation falls when the mean daily temperature is below 2 °C that precipitation is estimated to be in the form of snow. If precipitation if estimated to fall as snow then to simulate drifting, only 70% of the total precipitation is allowed to accumulate resulting in a 30% loss due to snow "blow off". If precipitation occurs as rain on an existing snow pack, it is added directly to the snow pack as SWE.
Soil moisture (reported during the growing season months only)
Soil moisture is measured as millimetres (mm) of plant available water. Plant available water is approximately half of the total water that can be measured in the soil. Soil moisture is reported on from May through to October.
The crop gets the moisture it requires from the reserve of soil moisture, which in turn is replenished by precipitation. Soil moisture is a valuable indicator of drought potential because it indicates the reserve of water available to the crop at a given point in time. During peak growing periods, soil moisture reserves are consumed quickly and must be replenished frequently by rainfall. Poor soil moisture reserves during peak water use indicate a high risk of immediate crop stress. Prolonged stress becomes drought and results in significant unrecoverable yield loss.
Because the climate varies across Alberta, comparing current moisture levels to normal levels provides a valuable indicator of drought risk that can be applied to all localities during the frost-free season. Current soil moisture levels are compared against soil moisture levels for the same day in each year from 1961 to present. The frequency of occurrence is computed based on the percentile points, using the same method that was used for similar maps that were generated for precipitation. The frequency of occurrence is then plotted using the same class scheme as is used in the long-term (hydrologic) drought map (see table above). Soil moisture reserves with a modifier of low, indicate a need for more precipitation to restore reserves.
Soil moisture needed to return to average spring or fall conditions
Soil moisture needed to return to normal spring or fall conditions is computed by subtracting average soil moisture (spring or fall), computed using model runs dating back from 1961 from current soil moisture conditions. This yields the amount of recharge needed to bring current soil moisture levels to average. Historic model runs are then analyzed to determine how many years since 1961 that soil moisture recharge was similar to or greater than that currently needed. The number of years that this occurred is then used to compute the probability of returning to average. However, currently this process is unable to account for snow currently existing on the ground and as such is not as accurate where snow packs exist.
Report prepared by the Drought Reporting Team
Ralph Wright, Daniel Itenfisu and Isabel Simons-Everett
Conservation & Development Branch & Program
Alberta Agriculture and Food
Edmonton, AB T6R 5T6
Contact: Ralph Wright; ph (780) 427-3556
This report was created on August 23, 2007.
Drought analysis is currently scheduled at monthly intervals between October 31and April 3, and twice monthly from May 1 to September 30. This report updates the previous report of July 28, 2007 |
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